Mantra: A2z

[Krakatuk]

Let's put here all the experience one has about rendering with Mantra. All sorts of renders: toon, photorealistic, non-photorealistic, exteriors, interiors.

Personally me, would like to understand, for now, the way GI in exteriors works, well in fact first of all - HOW DOES GI WORK IN MANTRA?

Target:

Render a scene with no lights, just lit by an environment with GI.

Here are two scenes (

testScene.rar

TS_Houdini.rar

Edited October 25, 2007 by Krakatuk

[3__]

cab.bgeo is missing. or you forgot to lock it.

[Krakatuk]

Yes, sorry, my fault.

Re-uploaded Houdini scene in the first post.

Edited October 25, 2007 by Krakatuk

[andrewc]

I've attached a scene file that is set up to give a roughly similar look to your vray render. The basic setup is to use PBR with an environment light and view-dependent photon maps to cache the diffuse indirect lighting (note that although caustic photon maps don't work with environment lights, view-dependent photon maps work with any kind of light). Here are a few tips:

* Use cusped normals on your geometry. Point normals on polygons can somtimes cause very strange results for PBR (facet SOP with cusp polygons)

* Make sure your normals point outward (reverse SOP)

* To get lighting that bounces around more (ie. to lighten up some of the black areas), use more diffuse bounces (PBR tab of photon_generate) and a shader with a high diffuse component (Plastic shop with diffuse at 1.8)

* To get only diffuse in the render, turn off specular in the shader (plastic shop)

* Control smoothness of the photon map with photon supersamples (PBR tab of mantra1) - this is increased to 50 from the default of 10 to get a cleaner render

To render the scene, render photon_generate then mantra1. You can switch to micropolygon PBR to see the difference between the two rendering engines. See help section "Rendering Engines" for how to control sampling quality.

Good luck!

Andrew

testScene.hip

[Rafal123]

cool thread, great idea Krakatuk, come on people share your experience

[Krakatuk]

OK, I played around PBR - it works, but this pic took about 40 minutes to render. So here's a question - how to optimize rendering settings for good time/quality?

Mantra1 used for photon map generating and according to help there I should play with settings for photons (as it is for secondary bounces) like: Photon Storage Count, View Photon Supersamples, Global Count. Does sampling have any effect here? Or it's only useful for primary bounces, because I noticed that noise disappears in Mantra2 (primaries) when I increase Pixel Samples and Min Ray Samples.

TS_Houdini.rar

[mrsmary]

there has to be some optimization. and i would like to know abaout it,otherwise those render times are not logical to me. one of the main comparision between maya and houdini is you have to have a mel power house if you want to do the same thing that, houdini does without coding. this time i gues one needs a render powerhouse to have sexy images. but i want to beleive that there is a trick out there to reduce those render times.

lot of videos are emerging at sesi these days,which i respect. on this topic abaout, serious optimization and tricks, even a pdf would be very handfull.

[3__]

there has to be some optimization. and i would like to know abaout it,otherwise those render times are not logical to me.

agreed. its much slower than it should be for this sort of thing.

have a look at this one for comparison:

http://www.bee-www.com/parthenon/index.htm

will try setting up for this test later.

-cpb

[Jason]

agreed. its much slower than it should be for this sort of thing.

have a look at this one for comparison:

http://www.bee-www.com/parthenon/index.htm

will try setting up for this test later.

-cpb

Please remember that PBR rendering is more complex than straight GI or IBL - although its easy to see why it's easy to confuse the two since the test scenes are set up similarly. If you want to get similar results to that render, be sure to not use PBR to achieve it. PBR is represents more complex light paths than GI

Be sure to use Raytracing or Micropolygon rendering - and use the VEX Global Illumination SHOP or something.

It would be excellent if Andrew or Mark of SESI could write a full explanation (and an accurate overview) of what PBR really is and how it differs with GI and so forth.

[shikung444]

Is there any way to have multiple diffuse bounces in mantra without using PBR?

Edit:

I've been poking around a bit in the rendering parameters interface and discovered in the Irradiance section : Max Gi Bounces (vm_gibounce)

I searched for this in the help, and it seems that it is not documented yet. I tried applying the parameter in the mantra node and set it to 2 or 3, but I didn't see any noticeable effect. When I set more than one diffuse bounce in mental ray's final gather (in xsi or max) there is a noticeable brightening in the shadow areas.

Edited November 29, 2007 by shikung444

[Jason]

Is there any way to have multiple diffuse bounces in mantra without using PBR?

Edit:

I've been poking around a bit in the rendering parameters interface and discovered in the Irradiance section : Max Gi Bounces (vm_gibounce)

I searched for this in the help, and it seems that it is not documented yet. I tried applying the parameter in the mantra node and set it to 2 or 3, but I didn't see any noticeable effect. When I set more than one diffuse bounce in mental ray's final gather (in xsi or max) there is a noticeable brightening in the shadow areas.

I might be mistaken but I think the way to get multiple diffuse bounces is via the pathtrace() VEX function. Honestly I have not used it yet... try it out:) and let us know!

[shikung444]

I might be mistaken but I think the way to get multiple diffuse bounces is via the pathtrace() VEX function. Honestly I have not used it yet... try it out:) and let us know!

From the documentation: pathtrace() vex function

Works like irradiance, but uses the physically based rendering (PBR) engine to do secondary bounces.

So do I have to switch the renderer to PBR to use this function? Or could I continue to use the standard micropolygon renderer and just call this particular PBR function in the material? And, to use this correctly, does my shader have to have the BSDF function (F) properly set up?

I found that in the GI light shader, along with ambient occlusion and full irradiance, there is a path tracing option. I'm thinking that this is same function Jason has mentioned. Then the question is, do I have to call this somehow from the light shader, or can I call it through the material?

I'll give it a try this weekend. Thanks so much Jason.

Edited November 30, 2007 by shikung444

[edward]

I think your best bet is to have the PBR engine turned on. As I understand it, you *must* have a BSDF function properly set up for PBR. I recall hearing that all the default surface shaders have the F output setup already. If in doubt, double check the VEX code.

[shikung444]

I think your best bet is to have the PBR engine turned on. As I understand it, you *must* have a BSDF function properly set up for PBR. I recall hearing that all the default surface shaders have the F output setup already. If in doubt, double check the VEX code.

Hi Edward and everyone,

Earlier in this thread Jason said:

"If you want to get similar results to that render, be sure to not use PBR to achieve it."

And indeed, full PBR is overkill for the shot I'm working on and I'm thinking that the render time for the animation would be too long.

I'm making an outdoor snow scene with a vops snow shader (made from scratch, not using the default shaders). I added a few things in the shader after the lighting model to reach a specific effect, and I was hoping not to need to set up the F output to match it. But I would like to get even one extra diffuse bounce as some of the snow was too dark in the shadows.

For the time being I just added something to artificially tint the darker areas, and it looks fine now, but only in one lighting condition.

And of course I was wanting to make an ultimate all-purpose fast rendering snow shader

[mark]

ive just been using a lighting model vop and connecting its diffuse and BSDF to the output vop. not sure if thats right or not. i only ever got a black surface when using PBR until i realised i had to connect the the BSDF.